Acidity varies widely among natural lakes.
At first this variation appears as simple differences in pH values among
lakes. A closer look reveals that the relative amounts of materials
that produce acidity in lakes determine both a lake's pH and its buffering capacity
or resistance to change in pH. In this lesson you use microcosms
and WOW data to explore factors that determine a lake's pH.

As a biologist, you have received an Environmental
Protection Agency grant to investigate acid deposition in Minnesota
lakes. Your first charge is to analyze CO2and dissolved oxygen of
lake specimens in the lab. Next, you need to analyze WOW data for evidence
that a lake may be affected by acid deposition.

Part 1 - pH in a
Microcosm

Knowledge Base
Prepare a brief statement that
provides a brief overview of acid deposition in lakes. Why does your
study require
analysis of pH and dissolved oxygen? How is your lab study related
to acid deposition in northern lakes?

Experimental DesignDescribe
how to use the following equipment to analyze your specimens and demonstrate
levels of pH that might occur naturally due to photosynthesis
and respiration
by aquatic plants and animals.

Data CollectionDevelop a plan for recording your measurements
so they will be useful for your analysis. Collect and record your measurements.

Data Management and AnalysisProduce a series of graphs to show your
results. Be sure to label axes and use titles and legends. What do your
results show?

Interpretation of ResultsHow do your results relate to acid deposition?
Are your measurements consistent with levels that might occur naturally
due to photosynthesis and respiration by aquatic plants and animals?
Did your experimental plan work? What suggestions do you have for other
researchers completing a similar study?

Reporting ResultsYou need to use your graphs and analysis
of results when you prepare your final presentation (after Part 2).
Begin to consider the best way to report your results. Your teacher
will specify the format for your presentation: written report, oral
presentation, poster, or multi-media presentation.

Part 2 - Effect
of pH in Lakes

Knowledge BaseReview your knowledge of pH in lakes.
Would pH change by depth? How? Would changes vary by season? Why? How
might the microcosm study relate to lakes? What pH levels might occur
naturally due to photosynthesis and respiration by aquatic plants and
animals?

Experimental DesignChoose a WOW lake where you could demonstrate
evidence of acid deposition. Why do you suspect acid deposition could
be demonstrated in this lake? What WOW measures should be used to demonstrate
acid deposition? Explain your rationale for using these measures?

Data CollectionDevelop a plan for recording your measurements
so they will be useful for your analysis. Collect and record your measurements.

Data Management and AnalysisCreate a graph(s) of your data. Be sure
to title your graph(s) and label axes. Do the results show evidence
of acid deposition?

Interpretation of ResultsWhat are your suggestions for maintaining
or improving the water quality of this lake as it may be subject to
increasing acid precipitation? Can your results be applied to other
area lakes? Why? What suggestions do you have for other researchers
completing a similar study?

Reporting ResultsUse the results of the microcosm study
and analysis of WOW data to create a poster, oral presentation, written
paper, or multi-media presentation about acid deposition. Be sure to
include your suggestions for maintaining or improving the water quality
of this lake and your suggestions for other researchers.